The poem consists of two nine-line stanzas of verse. Interestingly, if we examine this poem carefully, we can see the way in which Plath deliberately structured these two stanzas in order to develop our understanding both of the mirror in this poem, the speaker, and of the woman who is so attached to the mirror.
In the first stanza, we have a description of the mirror that the mirror itself gives us, focusing on its objective stance and how it has "no preconceptions," and how it only reflects "faithfully" everything that it sees. In the second stanza, however, in a marked departure from the first stanza, the mirror chooses to introduce itself through a metaphor, describing itself as a "lake." This allows the mirror to develop its relationship with the woman who is so fixated on her appearance, and also allows Plath to continue this metaphor in the second stanza until the terrifying image of the "terrible fish" that surfaces day by day emerges to close the poem. Structure is implictly linked to meaning through Plath's organisation of the two stanzas.